This invention relates to an optical detection system and particularly to one adapted for discriminating between right and left-hand screw thread profiles of a threaded part.
Threaded workpieces such as bolts and screws can have either right-hand or left-hand helixes formed on them. While right-hand threads are most commonly found on threaded parts, there are many applications where left-hand threads are used. For example, the wheel mounting studs on some motor vehicles are left-hand threaded on the right-hand side of the vehicle, which has been found to reduce the tendency for wheel mounting lug nuts to loosen during use. In some settings there is a tendency for right and left-hand threaded workpieces to become intermingled, for example, in a motor vehicle mass assembly environment. In the case of wheel mounting studs, it is difficult to distinguish the two threaded profiles without carefully examining each workpiece. Obvious problems result if the incorrect handedness of a threaded workpiece is used. For example, installation of the wrong handedness of a wheel stud would interfere with lug nut installation and would become a service problem during the life of the vehicle.
Numerous systems based on optics and acoustics are presently known for evaluating the profile of screw threads. These devices, however, are generally not adapted for examining the helix direction or handedness of the threads. Accordingly, in situations where a mixture of right and left-hand workpieces tend to become intermingled, it is common to have an individual inspection operator evaluate each workpiece visually, which imposes labor costs and cycle time penalties.
In view of the foregoing, there is a need to provide an automated system for evaluating the handedness of threaded workpieces. Such a device is provided in accordance with this invention which employs a pair of light beams directed generally tangent to the workpiece at angularly displaced positions. Photodetectors sense the beams after they pass across the workpiece. When the workpieces are advanced axially, outputs unique to each handedness of thread are provided, and thus a means for distinguishing between them is provided.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanied drawings.